In electrochemical elements, particularly in nonaqueous electrolytic secondary batteries that are chargeable and dischargeable and have a high energy density, introduction of novel high capacity active materials has been vigorously studied to further increase the energy density. As a specific example, there is development of active materials from lithium-cobalt oxide to lithium-nickel oxide for positive electrode, and from graphite to alloy materials including silicon, tin, and the like for negative electrode.
Usual nonaqueous electrolytic secondary battery using these active materials have a sealed structure in which a positive electrode and a negative electrode are usually laminated with a separator being placed therebetween to thereby constitute an electrode group, and after the electrode group is housed in a casing, an opening of the casing is sealed with a sealing member. In a case of employing such a sealed structure, the following two safety mechanisms are provided. First, in order to exhaust to the outside of the casing gas occurring at an accidental incident such as internal short-circuiting or high-temperature storage, for example, the sealing member is formed with an exhaust valve that operates when the internal pressure inside the casing reaches a predetermined pressure. Second, because a terminal provided on the sealing member is electrically connected to either one of the positive electrode and the negative electrode, and the casing is electrically connected to the other electrode, not only the sealing member is electrically insulated from the casing, but also both are electrically insulated from each other by disposing a perforated plate between the electrode group and the sealing member (for example, refer to Patent Document 1). The perforated plate is formed of, for example, a polyolefin resin such as a polyethylene resin or a polypropylene resin, or a phenol resin including an inorganic additive with a glass cloth serving as a base material, and the like.    Patent Document 1: Japanese Unexamined Patent Publication No. 2002-231314)
However, because the above-mentioned high-capacity active materials have a high potential, the quantity and rate of gas occurring at an accidental incident are considerable. Additionally, in a nonaqueous electrolytic secondary battery using these high-capacity active materials, a surplus volume inside the casing is reduced as small as possible in many cases in order to further increase the energy density, which causes the problem that if gas occurs forcibly, it is difficult to smoothly exhaust the gas to the outside of the casing due to a limited passage to the exhaust valve.